This invention pertains generally to a liquid medicine injection device used in medical applications and, more particularly, relates to a backflow prevention structure and a backflow prevention unit for a liquid medicine injection device which allows easy liquid medicine filling operation.
FIGS. 14A and 14B illustrate an example of a conventional liquid medicine injection device 100, which comprises a liquid medicine retaining vessel 110 containing a liquid medicine to be injected, a backflow prevention structure 120 provided at an opening of the liquid medicine retaining vessel 110 at its one end (right end as shown in FIGS. 14A and 14B), and a tip cover 130 which closes off the opening of the liquid medicine retaining vessel 110.
The liquid medicine retaining vessel 110 accommodates in its internal space a piston 111 which can move back and forth in sliding contact, and has a connecting sleeve 112 whose diameter is smaller than that of the liquid medicine retaining vessel 110 itself at its right end. The aforementioned backflow prevention structure 120 is fitted in the connecting sleeve 112. The tip cover 130 Is constructed of a socket portion 131 which is fitted over the connecting sleeve 112 such that the socket portion 131 will not come off the connecting sleeve 112, and an inlet tube 132 which extends outward from a right end of the socket portion 131 and has a smaller diameter than the socket portion 131. The inlet tube 132 is provided for inserting an injection tube 210 of an injector 200 which has a cylinder 230 for holding the liquid medicine to be refilled into the liquid medicine retaining vessel 110 and a piston 220 for forcing the liquid medicine out of the cylinder 230.
The liquid medicine retaining vessel 110 also has an outlet tube 113 extending from a right end surface of the liquid medicine retaining vessel 110 for discharging the liquid medicine therein. With a delivery pipe 114 connected to the outlet tube 113, the liquid medicine within the liquid medicine retaining vessel 110 is forced out through the outlet tube 113 and introduced into a human body through the delivery pipe 114, a flow rate regulator and a catheter as the piston 111 is moved rightward by an unillustrated drive mechanism.
The aforementioned backflow prevention structure 120 includes a support cylinder 121 which is fitted into the connecting sleeve 112 such that a curved outer surface of the support cylinder 121 can slide along a curved inner surface of the connecting sleeve 112, and a check valve 125 made of an rubber-like elastic material which is fitted concentrically in the support cylinder 121. The support cylinder 121 is provided with a support bar 122 situated on a central axis of the support cylinder 121, and the check valve 125 is fitted over the support bar 122. A plurality of rodlike stoppers 123 radially project from a curved outer surface of the support bar 122. Outer ends of these stoppers 123 are fixed to a curved inner surface of the support cylinder 121 so that the support bar 122 is located on the central axis of the support cylinder 121.
Also, an annular projection 115 jutting inward is formed at a root end of the curved inner surface of the connecting sleeve 112. This annular projection 115 prevents the support cylinder 121 from entering the interior of the liquid medicine retaining vessel 110.
The aforementioned check valve 125 is constructed of a cylindrical portion 126 whose diameter is slightly smaller than the inner diameter of the support cylinder 121 and a conical valve portion 127 having a solid truncated circular cone shape formed at a far end (right end as illustrated in FIGS. 14A and 14B) of the cylindrical portion 126. A plurality of ribs 128 running parallel to an axial direction are formed on the cylindrical portion 126 at regular intervals around its curved outer surface, and liquid medicine passages 300 are formed between these ribs 128.
The conical valve portion 127 is shaped such that it comes in contact with a conical slope 133 formed where a curved inner surface of the socket portion 131 and a curved inner surface of the inlet tube 132 meet when the tip cover 130 is fitted on the connecting sleeve 112. This makes it possible to securely prevent the liquid medicine in the liquid medicine retaining vessel 110 from leaking through the backflow prevention structure 120. Furthermore, there is formed a slotted groove 127a, through which the liquid medicine flows, in a projecting end (right end as illustrated in FIGS. 14A and 14B) of the conical valve portion 127 across the diameter of the projecting end.
According to the liquid medicine injection device 100 thus constructed, the liquid medicine is injected into the liquid medicine retaining vessel 110 as follows. First, the injection tube 210 of the injector 200 charged with the liquid medicine is inserted into the inlet tube 132 until a tip end of the injection tube 210 pushes the projecting end of the conical valve portion 127 inward as shown in FIG. 14A. Since the check valve 125 made of the rubber-like elastic material is deformed consequently, the projecting end of the conical valve portion 127 is forced into an internal space of the socket portion 131 of the tip cover 130 as shown in FIG. 14B. As a result, the liquid medicine passages 300 are formed in the backflow prevention structure 120 as shown by thick arrows in FIG. 14B. When the piston 220 of the injector 200 is pushed into the cylinder 230 in this condition, the liquid medicine within the cylinder 230 is injected into the liquid medicine retaining vessel 110 through the injection tube 210, the slotted groove 127a in the conical valve portion 127 and the liquid medicine passages 300 formed in a gap between the curved outer surface of the cylindrical portion 126 and the curved inner surface of the support cylinder 121. As the liquid medicine is injected in this fashion, the piston 111 in the liquid medicine retaining vessel 110 is caused to retract (leftward as illustrated).
When injection of the liquid medicine into the liquid medicine retaining vessel 110 is completed, the injection tube 210 of the injector 200 is pulled out of the inlet tube 132. Then, the check valve 125 which has been elastically deformed extends, or returns to its original shape, so that the conical valve portion 127 of the check valve 125 comes back into contact with the conical slope 133 of the tip cover 130 and thereby closes an opening in the tip cover 130 as shown in FIG. 14B. Therefore, the liquid medicine once introduced into the liquid medicine retaining vessel 110 will never leak to its exterior through the inlet tube 132.
In the above-described conventional liquid medicine injection device 100, the injection tube 210 of the injector 200 is pulled out of the inlet tube 132 when interrupting the injection of the liquid medicine into the liquid medicine retaining vessel 110 halfway or when the injection of the liquid medicine has been completed. If the injection tube 210 is pulled out quickly in such cases, the liquid medicine left in the liquid medicine passages 300 may flow out backward to the exterior through a gap between the conical slope 133 of the tip cover 130 and the conical valve portion 127 of the check valve 125 before the check valve 125 which has been reduced in length due to elastic deformation returns to its original length.
To avoid such a leakage problem, it would be necessary to pull the cylinder 230 (leftward as illustrated in FIGS. 14A and 14B) while exerting a pushing force on the piston 220 and, then, slowly extract the injection tube 210 out of the inlet tube 132. Such work is considerably difficult and impractical, however.
Furthermore, if the pushing force exerted on the piston 220 of the injector 200 is reduced during the injection of the liquid medicine into the liquid medicine retaining vessel 110, the liquid medicine once introduced into the liquid medicine retaining vessel 110 will flow back into the cylinder 230 through the slotted groove 127a due to internal pressure of the liquid medicine retaining vessel 110. It is therefore necessary to maintain the pushing force on the piston 220 of the injector 200 while injecting the liquid medicine, which is inconvenient and bothersome.